1. Field of the Invention
The present invention relates to radio frequency (RF) devices and, more particularly, to an integrated balun and coupler transformer.
2. Description of the Background Art
A balun is a device designed to convert between balanced radio frequency (RF) signals and unbalanced RF signals, such as between twin-lead (balanced line) and coaxial cables (unbalanced line). A balun is typically implemented through the use of a small isolation transformer, with the earth ground or chassis ground left floating on the balanced side. In such a configuration, the balun can also perform impedance matching. For example, baluns are used in amplifiers having a push-pull configuration in order to convert the balanced output signal to an unbalanced signal.
A coupler is a transmission device for sampling (through a known coupling loss) the signal in a transmission line. For example, couplers are used in electronic devices, such as amplifiers, to monitor output signal level and feed a sample to the control logic (e.g., automatic gain control (AGC) logic or other type of monitor circuit for further processing).
Some electronic devices, such as the exemplary amplifiers described above, require both a balun and a coupler at their outputs. Conventionally, the balun and the coupler are two separate devices. As such, they take up significant space, contribute added insertion loss, and compromise the output impedance match.